Current feed circuit for sensor coils in coordinate input device

Abstract

A current feed circuit for feeding a high-frequency current to a plurality of sensor coils in a coordinate input device includes a high-frequency signal transmitting circuit for generating a high-frequency current corresponding to a high-frequency signal input; a plurality of driver transistors, each being provided between the high-frequency signal transmitting circuit and each of a plurality of sensor coils for transmitting the high-frequency current to the corresponding sensor coil; and a plurality of switches, each being provided with respect to each of the plurality of driver transistors for turning on/off the corresponding driver transistor.

1. A current feed circuit for feeding a high frequency current to a plurality of sensor coils included in an electromagnetic inductive coordinate input device, the circuit comprising:
 a first high-frequency signal transmitting circuit for generating a first high-frequency current corresponding to a positive half-wave high-frequency signal input; 
 a second high-frequency signal transmitting circuit for generating a second high-frequency current corresponding to a negative half-wave high-frequency signal input; 
 a first plurality of driver transistors, each being provided between said first high-frequency signal transmitting circuit and each of a plurality of sensor coils for transmitting the first high-frequency current to the corresponding sensor coil; 
 a second plurality of driver transistors, each being provided between the second high-frequency signal transmitting circuit and each of a plurality of sensor coils for transmitting the second high-frequency current to the corresponding sensor coil; 
 a first plurality of switches, each being provided with respect to each of said first plurality of driver transistors for turning on/off the corresponding driver transistor; 
 a second plurality of switches, each being provided with respect to each of said second plurality of driver transistors for turning on/off the corresponding driver transistor; and 
 a circuit element for combining the first high-frequency current transmitted from said first plurality of driver transistors with the second high-frequency current transmitted from said second plurality of driver transistors to transmit the combined current to each of the plurality of sensor coils. 
 
   
   
     2. The current feed circuit of  claim 1 , wherein said first high-frequency signal transmitting circuit comprises a high-frequency signal generator and a separation circuit. 
   
   
     3. The current feed circuit of  claim 1 , wherein said first high-frequency signal transmitting circuit is an operational amplifier. 
   
   
     4. The current feed circuit of  claim 1 , wherein said second high-frequency signal transmitting circuit comprises a high-frequency signal generator and a separation circuit. 
   
   
     5. The current feed circuit of  claim 1 , wherein said second high-frequency signal transmitting circuit includes an operational amplifier. 
   
   
     6. The current feed circuit for sensor coils in a coordinate input device of  claim 1 , wherein each of said first plurality of driver transistors is cascade-connected to an output from said first high-frequency signal transmitting circuit, and each of said second plurality of driver transistors is cascade-connected to an output of said second high-frequency signal transmitting circuit. 
   
   
     7. The current feed circuit of  claim 1 , wherein said first plurality of driver transistors are connected in parallel with each other. 
   
   
     8. The current feed circuit of  claim 1 , wherein said second plurality of driver transistors are connected in parallel with each other. 
   
   
     9. The current feed circuit of  claim 1 , wherein said first and second high-frequency currents are generated using two power supplies. 
   
   
     10. The current feed circuit of  claim 1 , wherein said first and second high-frequency currents are generated using one power supply. 
   
   
     11. The current feed circuit of  claim 1 , wherein said first and second pluralities of driver transistors are selected from the group consisting of bipolar transistors and field effect transistors. 
   
   
     12. A current feed circuit for feeding a high-frequency current to a plurality of sensor coils included in an electromagnetic inductive coordinate input device, the circuit comprising:
 a high-frequency signal transmitting circuit for generating a high-frequency current corresponding to a high-frequency signal input; 
 a plurality of driver transistors, each being provided between said high-frequency signal transmitting circuit and each of a plurality of sensor coils for transmitting the high-frequency current to the corresponding sensor coil; and 
 a plurality of switches, each being provided with respect to each of said plurality of driver transistors for turning on/off the corresponding driver transistor. 
 
   
   
     13. The current feed circuit for sensor coils in a coordinate input device of  claim 12 , wherein each of said plurality of driver transistors is cascade-connected to the output of the high-frequency signal transmitting circuit. 
   
   
     14. The current feed circuit of  claim 12 , wherein said high-frequency signal transmitting circuit comprises a high-frequency signal generator and a separation circuit. 
   
   
     15. The current feed circuit of  claim 12 , wherein said high-frequency signal transmitting circuit includes a three-transistor current-mirror circuit. 
   
   
     16. The current feed circuit of  claim 12 , wherein said plurality of driver transistors are connected in parallel with each other. 
   
   
     17. The current feed circuit of  claim 12 , wherein said high-frequency current is generated using two power supplies. 
   
   
     18. The current feed circuit of  claim 12 , wherein said high-frequency current is generated using one power supply. 
   
   
     19. The current feed circuit of  claim 12 , wherein said driver transistors are selected from the group consisting of bipolar transistors and field effect transistors. 
   
   
     20. A current feed circuit method for feeding a high-frequency current to a plurality of sensor coils included in an electromagnetic inductive coordinate input device, comprising the steps of:
 generating a first high-frequency current corresponding to a positive half-wave high-frequency signal input; 
 generating a second high-frequency current corresponding to a negative half-wave high-frequency signal input; 
 combining the first high-frequency current with the second high-frequency current; 
 transmitting the combined current to a corresponding one of a plurality of sensor coils; 
 providing a first high-frequency signal transmitting circuit for generating the first high-frequency current; 
 providing a second high frequency signal transmitting circuit for generating the second high-frequency current; and 
 connecting a first plurality of driver transistors between the first high-frequency signal transmitting circuit and each of the plurality of sensor coils. 
 
   
   
     21. The method of  claim 20 , comprising the step of connecting a second plurality of driver transistors between second high-frequency signal transmitting circuit and each of the plurality of sensor coils. 
   
   
     22. The method of  claim 21 , including the step of providing a first plurality of switches, each one of the first plurality of switches for turning on/off one of the first plurality of driver transistors. 
   
   
     23. The method of  claim 22 , including the step of providing a second plurality of switches, each one of the second plurality of switches for turning on/off one of the second plurality of driver transistors. 
   
   
     24. The method of  claim 23 , including the step of providing a circuit element for combining the first high-frequency current with the second high-frequency current.